An attempt to photograph a real space with a photographing apparatus mounted on a mobile unit and represent the photographed real space as a virtual space based on the photographed real image data by using a computer (for instance, see Endo, Katayama, Tamura, Hirose, Watanabe and Tanigawa: “Building Image-Based Cybercities by Using Vehicle-Mounted Cameras” Society Conference of IEICE, PA-3-4, pp. 276 to 277, 1997 or Hirose, Watanabe, Tanigawa, Endo, Katayama and Tamura: “Building Image-Based Cybercities by Using Vehicle-Mounted Cameras (2)—Generation of Wide-Range Virtual Environment by Using Photorealistic Images—”, Proceedings of the Virtual Reality Society of Japan Second Annual Conference, and so on).
As a technique for representing a photographed real space as a virtual space based on real image data photographed by a photographing apparatus mounted on a mobile unit, a technique of reproducing a geometric shape model of a real space based on photographed image data and representing it by a conventional CG technology can be named, which is limited as to exactness, accuracy, reality of the model and so on. On the other hand, the Image-Based Rendering (IBR) technology that does not perform reproduction using a model but represents a virtual space by using a plurality of photographed images is receiving attention in recent years. The IBR technology is a technology for generating an image seen from an arbitrary point of view based on a plurality of photographed images. As the IBR technology is based on the photographed images, it can represent a realistic virtual space.
To construct a virtual space capable of walk-through by using such IBR technology, it is necessary to generate and present an image according to a position in the virtual space of a person experiencing it. Therefore, it is necessary to associate each frame of photographed image data with a position in the virtual space. However, as the virtual space is a space generated based on the real space here, the position in the virtual space is the position in the real space in other words. To be more specific, it is necessary to associate each frame of photographed image data with position data of the real space and know in which position in the real space each frame was photographed.
As a technique for acquiring position data in the real space, a positioning system using an artificial satellite represented by GPS (Global Positioning System) that is also used on car navigation systems is generally utilized. As a technique for associating photographed image data with position data acquired from GPS and so on, a method of associating it by using a time code is proposed (Japanese Patent Application Laid-Open No. 11-168754). This technique associates time data included in the position data with a time code added to each frame of photographed image data so as to associate each frame of the photographed image data with the position data.
However, in the case of GPS for instance, there is a possibility that position data cannot be acquired due to a geographical condition or an error included in the position data is too large to ignore. Therefore, as to a portion where the image data could not be associated with the position data or the association was incorrect, a technique for simply acquiring a position and associating it with the image data is sought.